Possible forcing of global temperature by the oceanic tides

An approximately decadal periodicity in surface air temperature is discernable in global observations from A.D. 1855 to 1900 and since A.D. 1945, but with a periodicity of only about 6 years during the intervening period. Changes in solar irradiance related to the sunspot cycle have been proposed to account for the former, but cannot account for the latter. To explain both by a single mechanism, we propose that extreme oceanic tides may produce changes in sea surface temperature at repeat periods, which alternate between approximately one-third and one-half of the lunar nodal cycle of 18.6 years. These alternations, recurring at nearly 90-year intervals, reflect varying slight degrees of misalignment and departures from the closest approach of the Earth with the Moon and Sun at times of extreme tide raising forces. Strong forcing, consistent with observed temperature periodicities, occurred at 9-year intervals close to perihelion (solar perigee) for several decades centered on A.D. 1881 and 1974, but at 6-year intervals for several decades centered on A.D. 1923. As a physical explanation for tidal forcing of temperature we propose that the dissipation of extreme tides increases vertical mixing of sea water, thereby causing episodic cooling near the sea surface. If this mechanism correctly explains near-decadal temperature periodicities, it may also apply to variability in temperature and climate on other times-scales, even millennial and longer.

The observed global warming record: What does it tell us?

Global, near-surface temperature data sets and their derivations are discussed, and differences between the Jones and Intergovernmental Panel on Climate Change data sets are explained. Global-mean temperature changes are then interpreted in terms of anthropogenic forcing influences and natural variability. The inclusion of aerosol forcing improves the fit between modeled and observed changes but does not improve the agreement between the implied climate sensitivity value and the standard model-based range of 1.5–4.5°C equilibrium warming for a CO2 doubling. The implied sensitivity goes from below the model-based range of estimates to substantially above this range. The addition of a solar forcing effect further improves the fit and brings the best-fit sensitivity into the middle of the model-based range. Consistency is further improved when internally generated changes are considered. This consistency, however, hides many uncertainties that surround observed data/model comparisons. These uncertainties make it impossible currently to use observed global-scale temperature changes to narrow the uncertainty range in the climate sensitivity below that estimated directly from climate models.

DEG/ENaC ion channels involved in sensory transduction are modulated by cold temperature

Several DEG/ENaC cation channel subunits are expressed in the tongue and in cutaneous sensory neurons, where they are postulated to function as receptors for salt and sour taste and for touch. Because these tissues are exposed to large temperature variations, we examined how temperature affects DEG/ENaC channel function. We found that cold temperature markedly increased the constitutively active Na+ currents generated by epithelial Na+ channels (ENaC). Half-maximal stimulation occurred at 25°C. Cold temperature did not induce current from other DEG/ENaC family members (BNC1, ASIC, and DRASIC). However, when these channels were activated by acid, cold temperature potentiated the currents by slowing the rate of desensitization. Potentiation was abolished by a “Deg” mutation that alters channel gating. Temperature changes in the physiologic range had prominent effects on current in cells heterologously expressing acid-gated DEG/ENaC channels, as well as in dorsal root ganglion sensory neurons. The finding that cold temperature modulates DEG/ENaC channel function may provide a molecular explanation for the widely recognized ability of temperature to modify taste sensation and mechanosensation.

Global climate change

Most of the last 100,000 years or longer has been characterized by large, abrupt, regional-to-global climate changes. Agriculture and industry have developed during anomalously stable climatic conditions. New, high-resolution analyses of sediment cores using multiproxy and physically based transfer functions allow increasingly confident interpretation of these past changes as having been caused by “band jumps” between modes of operation of the climate system. Recurrence of such band jumps is possible and might be affected by human activities.

Membrane lipid perturbation modifies the set point of the temperature of heat shock response in yeast.

Addition of a saturated fatty acid (SFA) induced a strong increase in heat shock (HS) mRNA transcription when cells were heat-shocked at 37 degrees C, whereas treatment with an unsaturated fatty acid (UFA) reduced or eliminated the level of HS gene transcription at 37 degrees C. Transcription of the delta 9-desaturase gene (Ole1) of Histoplasma capsulatum, whose gene product is responsible for the synthesis of UFA, is up-regulated in a temperature-sensitive strain. We show that when the L8-14C mutant of Saccharomyces cerevisiae, which has a disrupted Ole1 gene, is complemented with its own Ole1 coding region under control of its own promoter or Ole1 promoters of H. capsulatum, the level of HS gene transcription depends on the activity of the promoters. Fluorescence anisotropy of mitochondrial membranes of completed strains corresponded to the different activity of the Ole1 promoter used. We propose that the SFA/UFA ratio and perturbation of membrane lipoprotein complexes are involved in the perception of rapid temperature changes and under HS conditions disturbance of the preexisting membrane physical state causes transduction of a signal that induces transcription of HS genes.

Drought-induced shift of a forest–woodland ecotone: Rapid landscape response to climate variation

In coming decades, global climate changes are expected to produce large shifts in vegetation distributions at unprecedented rates. These shifts are expected to be most rapid and extreme at ecotones, the boundaries between ecosystems, particularly those in semiarid landscapes. However, current models do not adequately provide for such rapid effects—particularly those caused by mortality—largely because of the lack of data from field studies. Here we report the most rapid landscape-scale shift of a woody ecotone ever documented: in northern New Mexico in the 1950s, the ecotone between semiarid ponderosa pine forest and piñon–juniper woodland shifted extensively (2 km or more) and rapidly (<5 years) through mortality of ponderosa pines in response to a severe drought. This shift has persisted for 40 years. Forest patches within the shift zone became much more fragmented, and soil erosion greatly accelerated. The rapidity and the complex dynamics of the persistent shift point to the need to represent more accurately these dynamics, especially the mortality factor, in assessments of the effects of climate change.

Two terrestrial records of rapid climatic change during the glacial–Holocene transition (14,000– 9,000 calendar years B.P.) from Europe

Two independent multidisciplinary studies of climatic change during the glacial–Holocene transition (ca. 14,000–9,000 calendar yr B.P.) from Norway and Switzerland have assessed organism responses to the rapid climatic changes and made quantitative temperature reconstructions with modern calibration data sets (transfer functions). Chronology at Kråkenes, western Norway, was derived from calibration of a high-resolution series of 14C dates. Chronologies at Gerzensee and Leysin, Switzerland, were derived by comparison of δ18O in lake carbonates with the δ18O record from the Greenland Ice Core Project. Both studies demonstrate the sensitivity of terrestrial and aquatic organisms to rapid temperature changes and their value for quantitative reconstruction of the magnitudes and rates of the climatic changes. The rates in these two terrestrial records are comparable to those in Greenland ice cores, but the actual temperatures inferred apply to the terrestrial environments of the two regions.

Remodeling of Yeast Genome Expression in Response to Environmental Changes

We used genome-wide expression analysis to explore how gene expression in Saccharomyces cerevisiae is remodeled in response to various changes in extracellular environment, including changes in temperature, oxidation, nutrients, pH, and osmolarity. The results demonstrate that more than half of the genome is involved in various responses to environmental change and identify the global set of genes induced and repressed by each condition. These data implicate a substantial number of previously uncharacterized genes in these responses and reveal a signature common to environmental responses that involves ∼10% of yeast genes. The results of expression analysis with MSN2/MSN4 mutants support the model that the Msn2/Msn4 activators induce the common response to environmental change. These results provide a global description of the transcriptional response to environmental change and extend our understanding of the role of activators in effecting this response.

An evaluation of the performance of cDNA microarrays for detecting changes in global mRNA expression

The cDNA microarray is one technological approach that has the potential to accurately measure changes in global mRNA expression levels. We report an assessment of an optimized cDNA microarray platform to generate accurate, precise and reliable data consistent with the objective of using microarrays as an acquisition platform to populate gene expression databases. The study design consisted of two independent evaluations with 70 arrays from two different manufactured lots and used three human tissue sources as samples: placenta, brain and heart. Overall signal response was linear over three orders of magnitude and the sensitivity for any element was estimated to be 2 pg mRNA. The calculated coefficient of variation for differential expression for all non-differentiated elements was 12–14% across the entire signal range and did not vary with array batch or tissue source. The minimum detectable fold change for differential expression was 1.4. Accuracy, in terms of bias (observed minus expected differential expression ratio), was less than 1 part in 10 000 for all non-differentiated elements. The results presented in this report demonstrate the reproducible performance of the cDNA microarray technology platform and the methods provide a useful framework for evaluating other technologies that monitor changes in global mRNA expression.

Changes of Mitochondrial Properties in Maize Seedlings Associated with Selection for Germination at Low Temperature. Fatty Acid Composition, Cytochrome c Oxidase, and Adenine Nucleotide Translocase Activities1

Mitochondria are affected by low temperature during seedling establishment in maize (Zea mays L.). We evaluated the associated changes in the mitochondrial properties of populations selected for high (C4-H) and low (C4-L) germination levels at 9.5°C. When seedlings of the two populations were grown at 14°C (near the lower growth limit), the mitochondrial inner membranes of C4-H showed a higher percentage of 18-carbon unsaturated fatty acids, a higher fluidity, and a higher activity of cytochrome c oxidase. We found a positive relationship between these properties and the activity of a mitochondrial peroxidase, allowing C4-H to reduce lipid peroxidation relative to C4-L. The specific activity of reconstituted ATP/ADP translocase was positively associated with this peroxidase activity, suggesting that translocase activity is also affected by chilling. The level of oxidative stress and defense mechanisms are differently expressed in tolerant and susceptible populations when seedlings are grown at a temperature near the lower growth limit. Thus, the interaction between membrane lipids and cytochrome c oxidase seems to play a key role in maize chilling tolerance. Furthermore, the divergent-recurrent selection procedure apparently affects the allelic frequencies of genes controlling such an interaction.

Changes in global gene expression patterns during development and maturation of the rat kidney

We set out to define patterns of gene expression during kidney organogenesis by using high-density DNA array technology. Expression analysis of 8,740 rat genes revealed five discrete patterns or groups of gene expression during nephrogenesis. Group 1 consisted of genes with very high expression in the early embryonic kidney, many with roles in protein translation and DNA replication. Group 2 consisted of genes that peaked in midembryogenesis and contained many transcripts specifying proteins of the extracellular matrix. Many additional transcripts allied with groups 1 and 2 had known or proposed roles in kidney development and included LIM1, POD1, GFRA1, WT1, BCL2, Homeobox protein A11, timeless, pleiotrophin, HGF, HNF3, BMP4, TGF-α, TGF-β2, IGF-II, met, FGF7, BMP4, and ganglioside-GD3. Group 3 consisted of transcripts that peaked in the neonatal period and contained a number of retrotransposon RNAs. Group 4 contained genes that steadily increased in relative expression levels throughout development, including many genes involved in energy metabolism and transport. Group 5 consisted of genes with relatively low levels of expression throughout embryogenesis but with markedly higher levels in the adult kidney; this group included a heterogeneous mix of transporters, detoxification enzymes, and oxidative stress genes. The data suggest that the embryonic kidney is committed to cellular proliferation and morphogenesis early on, followed sequentially by extracellular matrix deposition and acquisition of markers of terminal differentiation. The neonatal burst of retrotransposon mRNA was unexpected and may play a role in a stress response associated with birth. Custom analytical tools were developed including “The Equalizer” and “eBlot,” which contain improved methods for data normalization, significance testing, and data mining.

Dependence of global temperatures on atmospheric CO2 and solar irradiance

Changes in global average temperatures and of the seasonal cycle are strongly coupled to the concentration of atmospheric CO2. I estimate transfer functions from changes in atmospheric CO2 and from changes in solar irradiance to hemispheric temperatures that have been corrected for the effects of precession. They show that changes from CO2 over the last century are about three times larger than those from changes in solar irradiance. The increase in global average temperature during the last century is at least 20 times the SD of the residual temperature series left when the effects of CO2 and changes in solar irradiance are subtracted.